The present invention relates to apparatus and methods for balancing turbine rotors and particularly relates to balancing turbine rotors without deforming or otherwise penetrating the rotor component to which a balance weight is secured.
A traditional method for balancing a rotor for a turbine, for example, a gas turbine, is to provide a 360xc2x0 circumferential balance groove in one or more of the rotational components at locations corresponding to as large a radius as possible. These balance grooves are typically configured to lie in vertical planes normal to the rotor axis on the axial faces and circumferential rims of rotary components of the rotor, e.g., wheels and spacers. Conventionally, balance weights are then installed in the axial facing balance grooves of such components to counterbalance any imbalance that may exist in such individual components prior to assembly of the rotor. After assembly, spool balance weights are provided in the circumferential grooves to balance the rotor spool. After assembly of the buckets on the wheel rims, the rotor is finally balanced using weights applied to the circumferential grooves.
Typically, each of the circumferential and axially facing grooves has a generally dovetail configuration for receiving a complementary-shaped balance weight. In the axial facing vertical groove, each balance weight features an angled screw with a portion of the dovetail along the underside of the complementary-shaped balance weight removed so that the screw can be tightened into the corner of the groove to effectively hold the balance weight in the groove and without motion relative to the rotary component. In a circumferential, i.e., horizontal groove, a threaded opening is provided centrally through the balance weight and a screw fastener threads through the opening and bears against the base of the groove to secure the dovetail-shaped balance weight in the complementary-shaped groove. In each case, the rotary component and balance weight are staked to one another to prevent relative motion therebetween.
While these balance weight and slot combinations have proved effective, a potential remains for creating or inducing cracks in the rotary component upon its deformation by staking the component and balance weight to one another. Consequently, there has developed a need for a balance weight/groove combination for balancing rotary components and rotor assemblies in turbines which holds the balance weight against motion relative to the rotary component without staking the component and balance weight to one another and without otherwise deforming the material of the rotary component.
In accordance with the present invention, apparatus and methods are provided for balancing rotary components and rotor assemblies of a turbine without deforming, particularly without staking, the rotary component yet preventing movement of the balance weight and component relative to one another. To accomplish the foregoing, the rotary component is provided with a generally dovetail-shaped groove, e.g., in an axial face of the component normal to the axis of rotation of the component and in a rim extending circumferentially about the axis of rotation. Each groove has a projecting rail or rib along the base of the groove. A plurality of slots or recesses are formed in the rib at spaced circumferential locations one from the other about the groove. The groove also has one or more loading apertures where the side walls of the groove are spaced further from one another than remaining portions of the groove to enable insertion of one or more balance weights into the groove. The balance weights are preferably complementary in shape to the shape of the groove, i.e., dovetail-shaped. Each weight has a recess along its underside extending from end-to-end whereby, upon insertion of the balance weight into the dovetail groove, the weight can slide circumferentially along the groove to a selected location in registration with a slot.
At the selected location, a threaded fastener is extended through the balance weight into the slot for engagement against a base of the slot to preclude circumferential movement of the balance weight relative to the rotary component. To ensure against unthreading movement of the fastener, the balance weight and fastener are secured to one another, in addition to their threaded securement, for example, by staking. In this manner, the prior requirement for staking the rotary component and balance weight to one another is entirely eliminated, in turn eliminating the potential for crack formation in the rotary component as a result of staking the balance weight and rotary component to one another. Also, the weight can be adjusted by removing material adjacent an end thereof whereby substantially an infinite adjustment in locating the weight can be accomplished.
In a preferred embodiment according to the present invention, there is provided apparatus for balancing a turbine rotor about an axis of rotation, comprising a turbine component having a generally annular dovetail-shaped groove in a plane normal to the axis of rotation, a rib projecting outwardly of a base of the groove and having slots at spaced locations therealong interrupting the rib, a balance weight receivable in the groove and having a recess along an underside thereof for receiving the projecting rib of the groove, the balance weight having an opening therethrough between inner and outer sides thereof and a fastener in the opening having an end thereof engaging the groove in the slot, the fastener and the balance weight being staked to one another to secure the fastener and the balance weight to one another.
In a further preferred embodiment of the present invention, there is provided apparatus for balancing a turbine rotor about an axis of rotation comprising a plurality of wheels and spacers alternately stacked against one another and forming the rotor, at least one each of the wheels and spacers having a generally dovetail-shaped groove thereabout in a plane normal to the axis of rotation thereof, a rib projecting outwardly of a base of each groove, each rib being interrupted at circumferentially-spaced locations thereabout forming slots in the rib, a balance weight receivable in each groove, and having a recess along an underside thereof for receiving the projecting rib of the groove, each balance weight having an at least partially threaded opening therethrough between an outer side thereof and the underside and a threaded fastener threadedly engaging in each partially threaded opening and having an end thereof engaging said groove in the slot and means for securing the fastener and the balance weight to one another other than by the threaded engagement therebetween.
In a still further preferred embodiment according to the present invention, there is provided a method of balancing a turbine rotor about an axis of rotation wherein the rotor has a groove thereabout in a plane normal to the axis of rotation and a balance weight slidable along the groove into a predetermined location, comprising the steps of forming an outwardly projecting rib along a base of and substantially coextensively with the groove, forming a balance weight loading aperture in the groove, inserting a balance weight into the loading aperture, the balance weight having a recess extending from end-to-end thereof for receiving the rib of the rotor groove, providing slots in the rib at selected locations therealong, sliding the balance weight from the loading aperture along the groove into a selected location along the groove, threading a fastener through a complementary threaded opening in the balance weight into the slot and engaging a base of the slot to preclude circumferential displacement of the balance weight along the groove and securing the fastener and the balance weight to one another other than by the threaded engagement therebetween.